Unit 10 Flashcards
What is a virus?
A virus is a particle that can direct the processes of life, but it is not alive. They have acellular particles and no cytoplasm or organelles. Nor do they have metabolic processes, meaning that they are intracellular parasites.
What is the structure of a virus?
There is a capsid that surrounds the genome. The genome can be either RNA or DNA, but not both. There is also an optional envelope which is stolen from the host membrane (except pox).
What is a virion?
An extracellular form of a virus that can also be referred to as a virus particle.
What are the contents of a nucleocapsid?
DNA or RNA, structural proteins/protein shell, enzymes and nucleic acid binding proteins.
What is it called when the nucleocapsid is the outer structure?
“Naked” virus.
What is the class of virus when the nucleocapsid is covered with a plasma membrane?
Enveloped virus. The viral proteins project out of the membrane for attachment (peplomers, spikes, VAPS).
What is the nucleocapsid structure?
Capsomeres, Helical (rod) or icosahedral (geometric sphere). Bacteriophages have additional structures attached to the nucleocapsid “head”.
Where do enveloped viruses get their envelopes?
From the host cell membrane when budding out. The envelopes need moisture and are commonly spread through airborne droplets, secretions, organ transplants and blood transfusions.
How sensitive are enveloped viruses compared to naked capsid viruses?
Enveloped viruses need moisture to be spread and are much more sensitive. However, they may require CMI to clear because the humoral may not “see” them. On the other hand, naked capsid viruses are more resistant to acid, disinfectants, detergents, proteases and drying. And they spread much more easily.
How sensitive are enveloped viruses compared to naked capsid viruses?
Enveloped viruses need moisture to be spread and are much more sensitive. However, they may require CMI to clear because the humoral may not “see” them. On the other hand, naked capsid viruses are more resistant to acid, disinfectants, detergents, proteases and drying. And they spread much more easily.
What are the major steps in viral replication?
Attachment, penetration, synthesis, assembly and release.
Describe viral attachment and compare to bacteriophages.
Viral attachment involves cell surface receptors such as proteins, carbs, glycoproteins, glycolipids and lipids for recognition. For bacteriophages, the tail fibers allow attachment.
Describe viral penetration and compare to bacteriophages.
a
What are the major steps in viral replication?
Attachment, penetration, synthesis, assembly and release. (may need to add an uncoating or budding steps)
Describe viral penetration and compare to bacteriophages.
Bacteriophages inject genetic material and stay on the outside. Bacteria have primitive immune systems in which restriction endonucleases tthat chop up foreign DNA to protect agains bacteriophages. Animal viruses, on the other hand, are often taken up by endocytosis and the virus must then uncoat.
Describe viral synthesis and compare to bacteriophages.
For bacteriophages, all steps occur in the cytoplasm due to the fact that prokaryotes don’t have a nucleus. In animal viruses, DNA viruses replicate DNA in the nucleus and use ribosomes in the cytoplasm. RNA viruses with a positive sense RNA use it as a mRNA to make proteins right away. RNA viruses with a negative sense RNA use it to transcribe mRNA in the nucleus and then the proteins are made in the cytoplasm.
Describe viral assembly and compare to bacteriophages.
Depends on the virus type and not the prokaryotic/eukaryotic cell structure. Viruses self assemble in the cytoplasm of the host cell. Some eukaryotic viruses need envelopes from the host cell, so there is not a complete assembly until they bud out.
Describe viral release and compare to bacteriophages.
Some viruses lyse the host cell, while others don’t. Bacteriophages have a lytic cycle in which the host cell is killed when the virus lyses it. Then, there is the lysogenic cycle in which viral DNA is integrated into the host cell. The host may be protected from other viruses, but it is a ticking time bomb and can enter the lytic cycle. Eukaryotic viruses infections can lead to lysis OR budding and if a cell is chronically infected it is called a latent infection.
What criteria are used to classify viruses?
Size, morphology and nucleic acid content or structure (enveloped or naked capsid) or diseases caused (hepatitis viruses) or means of transmission (vectors) or host cell (animal, plant, bacterial)
What is the Baltimore system?
The most used classification. Groups viruses into 7 families and is based on genome structure considering biochemical characteristics, viral structure and mode of replication.
What is tropism?
Host cell-type specificity. Of
What is tropism?
Host cell-type specificity. Often determined by VAP’s on virus and receptors on host cells. Ex: Hep C is hepatotropic.
What is tropism?
Host cell-type specificity. Often determined by VAP’s on virus and receptors on host cells. Ex: Hep C is hepatotropic.
What is host range?
Species that a virus can infect. Many viruses have narrow host ranges with only one species. Others can infect many species, such as rabies.
What is viral burst size?
The number of virions produced when a cell lyses. Ranges from a few to 1000’s. May be expressed per replication cycle.
What is replication cycle?
The process that starts when a virion gets into a cell and ends when new virions are released. In human viruses a replication cycle is 8-40 hours. Bacteriophages can complete a replication cycle in as short as 20 minutes.
Differentiate between early and late viral proteins.
Biosynthesis happens in steps. Once a virus is in a host cell, it starts making proteins that it will need for replication, these are often the enzymes that the host lacks and are called EARLY PROTEINS. Then, the cell makes the rest of the proteins needed to assemble virions, including capsomeres to make up capsids. These are the LATE proteins. More complex viruses may have middle proteins.
What are the 7 classes according to Baltimore classification?
dsDNA ssDNA dsRNA \+ sense ssRNA - sense ssRNA RNA reverse transcribing DNA reverse transcribing.
What are the common dsDNA viruse families?
Adenoviridae, Poxviridae, Herpesviridae (HSV1 and 2, Varicella Zoster, EBV, CMV), Papillomaviridae.
What is the ssDNA virus?
Parvoviridae
What is the reverse DNA family?
Hepadnaviridae
Whate re the + ssRNA virus families?
Coronaviridae, picornaviridae, togaviridae, flaviviridae, caliciviridae.
What are the
s
What are the common dsDNA viruse families?
Adenoviridae (Adenovirus), Poxviridae (Small Pox), Herpesviridae (HSV1 and 2, Varicella Zoster, EBV, CMV), Papillomaviridae (HPV).
What is the ssDNA virus?
Parvoviridae (Parvovirus
What is the reverse DNA family?
Hepadnaviridae (Hep B)
Whate re the + ssRNA virus families?
Coronaviridae (SARS), picornaviridae (Poliovirus), togaviridae (Rubella), flaviviridae (Hep C, Yellow fever, West Nile), caliciviridae (Norwalk, Hep E).
What are the - ssRNA virus families?
Paramyxoviridae (Measles, mumps, RSV), Orthomyxoviridae (Influenza), Rhabdoviridae (Rabies), Flioviridae (Ebola, Marburg), Bunyaviridae (Hanta) Arenaviridae (LCMV).
What are the dsRNA virus families?
Reoviridae (Rotavirus)
What are the Reverse RNA virus familes?
Retroviridae (HIV)
Differentiate between the replication strategies of RNA and DNA viruses.
DNA replication is exclusively nuclear (except for POX)
Differentiate between + and - strand RNA viruses. What about Retroviruses.
For - sense, the first step is to transcribe the - sense RNA to produce mRNA’s which is a template for genome replication. For + sense RNA, it is directly translated into a protein product. Retroviruses does not serve as mRNA but as a template for reverse transcription.
What unique problem is presented to viruses using eukaryotic ribosomes? How does HIV adapt?
Viruses often have polycistronic mRNA’s. Eukaryotic host cell translation protein synthesis machinery in general uses monocistronic mRNA’s. Thus, the RNA’s have to solve this problem. The virus itself makes several monocistronic mRNA’s. The host splicing machinery cleaves the viral mRNA into more than one monocistronic RNA. A long polyprotein is made that is then cut into separate proteins. Viral mRNA has sites fro ribosomes internally and at the 5’ end.
